The present invention relates to semiconductor integrated circuits and a method of fabrication thereof, with particular application to a selective dry etch process of block copolymers used in directed self-assembly (DSA) processes. More particularly, the dry etch process includes gas pulsing carbon-monoxide based plasmas to selectively remove one block polymer in the block copolymer.
Block copolymer lithography is becoming an established DSA technique for patterning beyond optical lithography applications. DSA is based on combining the intrinsic property of block copolymers to phase separate at the molecular scale with the capabilities of conventional top-down lithographic methods for patterning surfaces. Guiding the self-assembly of block copolymers by surface modification is one of the most used processes to drive the self-assembly in a convenient way. It typically consists of using lithography and an oxygen based plasma to create different wettability regions on a polymer brush material grafted onto the surface.
The directed self-assembly can be a graphoepitaxy process or chemoepitaxy process. In the graphoepitaxy process, the self-organization of the block copolymers is guided by topographical guiding patterns such that the block copolymer self-organizes in useful domains, which is dominated by the concept of confinement. Neutral walls or pillars that define the guiding pattern prevent certain chain configurations, which then lead to the polymer adjusting its periodic structure along a pre-determined axis. In the chemoepitaxy process, local variations in the surface energy of the layer to which the DSA material is applied dictate how the block copolymers will align. Through subsequent selective removal of one polymer type, a patterned structure of gaps is formed which can be used in a manner similar to a resist layer on the underlying substrate.